Heat exchanger with enhanced heat transfer

ABSTRACT

A heat exchange device includes a plurality of flow passages. Each flow passage has an inlet and an outlet configured for hot fluid flow in a direction from the inlet to the outlet. Secondary heat transfer elements within and adjacent each flow passage have heat transfer characteristics varying in the direction of the hot fluid flow such that peak metal temperatures limit creep to acceptable values and such that transient thermal stresses are limited to values producing acceptable life of the device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to heat exchangers, and more particularly to plate-stack heat exchangers.

2. Description of Related Art

Heat exchangers such as, for example, tube-shell heat exchangers, are typically used in aerospace turbine engines and other high temperature applications. These heat exchangers are used to transfer thermal energy between two fluids without direct contact between the two fluids. In particular, a primary fluid is typically directed through a fluid passageway of the heat exchanger, while a cooling or heating fluid is brought into external contact with the fluid passageway. In this manner, heat may be conducted through walls of the fluid passageway to thereby transfer energy between the two fluids. One typical application of a heat exchanger is related to an engine and involves the cooling of air drawn into the engine and/or exhausted from the engine.

However, typical tube shell design heat exchangers have structural issues when their cantilevered tube bundles are exposed to typical aerospace vibration environments. In addition, there can be bypass of flow around the tubes on the low pressure side of the heat exchanger, resulting in reduced thermal effectiveness as well as other adverse system impacts such as excessive low pressure flow.

Traditional plate-stack heat exchangers are also used in high temperature applications and address some of the aforementioned structural and flow bypass issues. In prior art applications, plate stack heat exchangers have been designed to have a large product of heat transfer coefficient and heat transfer surface area to achieve a large amount of heat transfer in a small volume. However, as this product of heat transfer coefficient and heat transfer surface area increases on the hot side of a plate stack heat exchanger, the metal temperature increases.

As peak operating temperatures of both tube shell and plate stack heat exchangers is increased in high temperature applications, these prior art heat exchangers operate at conditions such that metal temperatures in the hottest regions of the device, specifically where the hot inlet flow and cold outlet flow are in closest proximity are close enough to the metal melting point that creep of the material occurs, significantly shortening the life of the prior art device. Creep is a phenomenon whereby the material at high temperatures deforms plastically at stresses below the yield strength of the material. Furthermore, rapid changes in temperatures of one or both of the heat transfer fluids flowing through the heat exchanger result in large thermal gradients and large resultant stresses and strains into the plastic region of the heat exchanger material, resulting in reduced life of the heat exchanger. These thermal gradients are typically largest near the hottest portion of the heat exchanger.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved heat exchangers with reduced peak metal temperatures and reduced thermal gradients in the metal of these devices during thermal transients. The present disclosure provides a solution for this need.

SUMMARY OF THE INVENTION

A heat exchange device includes a plurality of flow passages. Each flow passage has an inlet and an outlet configured for hot fluid flow in a direction from the inlet to the outlet. Secondary heat transfer elements within and adjacent each flow passage have heat transfer characteristics varying in the direction of the hot fluid flow such that peak metal temperatures limit creep to acceptable values and such that transient thermal stresses are limited to values producing acceptable life of the device.

The heat transfer elements can be positioned proximate the inlet and the outlet and gradually transition from straight heat transfer elements at the inlet to shaped heat transfer elements proximate the outlet. Proximate the inlet of each flow passage can include a first predetermined number of straight heat transfer elements. An intermediate section between the inlet and outlet of the flow passage can include a second predetermined number of straight heat transfer elements and a third predetermined number of shaped heat transfer elements, wherein the second predetermined number is greater than the first predetermined number. Proximate the outlet of the flow passage can include a fourth predetermined number of shaped heat transfer elements greater than the third predetermined number of shaped heat transfer elements.

The device can further include a first section and a second section. Each of the first and second sections including the flow passages, wherein each flow passage includes heat transfer elements positioned to provide increased heat transfer in a direction from the inlet to the outlet. The first and second sections can include plate sections in a stacked arrangement with each of the flow passages having a bend at an outer edge of the heat exchange device configured to return high pressure fluid to a center manifold. The center manifold can include a first plenum at one end configured to allow fluid to enter the center manifold and a second plenum on the opposing side configured to allow fluid to exit the center manifold. Hot fluid can flow through the first plenum into an inlet of a respective flow passage within the first and second sections, enters the center manifold through and outlet of the respective flow passage, and exits the center manifold through the second plenum.

A heat exchange device includes a first section and a second section. Each of the first and second sections including flow passages configured to cool fluid, each of the flow passages having an inlet and outlet wherein each flow passage includes heat transfer fins positioned proximate the inlet to the outlet and gradually transition from straight fins at the inlet to shaped fins proximate the outlet. A center manifold disposed between the first and second sections, wherein hot fluid enters the manifold at a first plenum, passes through the first and second sections and exits the center manifold at a second plenum.

These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:

FIG. 1 is a perspective view of a prior art heat exchanger, showing fins within flow passages forming flow channels between the fins;

FIG. 1A is a cross-sectional view of prior art fins of FIG. 1, showing only shaped fins;

FIG. 2 is an exemplary embodiment of fins constructed in accordance with the present disclosure, showing the transition between straight fins to shaped fins within the flow passage; and

FIG. 3 is a perspective view of a heat exchange device, showing first and second sections and a center manifold.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a heat exchange device in accordance with the disclosure is shown in FIG. 2 and is designated generally by reference character 100. Other embodiments of the heat exchange device in accordance with the disclosure, or aspects thereof, are provided in FIGS. 1-3, as will be described. The systems and methods described herein can be used in turbine engines exposed to high pressure and high temperatures, for example in aerospace application. The present disclosure provides for a device that reduces the product of heat transfer coefficient and heat transfer surface area in regions of the device where metal temperatures must be limited to meet life requirements, while still maintaining a large product of heat transfer coefficient and heat transfer surface area where large amounts of heat transfer per unit heat exchanger volume and weight can be achieved with reasonably low metal temperatures from a structural perspective between the hot and cold fluids.

With reference to FIGS. 1 and 1A a typical heat exchanger known in the prior art is shown. Hot fluid enters through an inlet 20 at one end and passes through fin channels in flow passages to an outlet 22 at an opposing end. Cold fluid is passed surrounding the flow passages to transfer heat between the hot fluid within the flow passages and the cold fluid. Typical heat exchangers include secondary heat transfer elements, such as fins 10, within each flow passage. As shown in FIG. 1 and in more detail in FIG. 1A, generally these fins extend from the inlet 20 to the outlet 22 and are equal in dimensions throughout the length of the flow passage 10. As shown in FIG. 1A, fins 10 are herringbone fins that extend from the inlet 20 to the outlet 22.

In contrast, with reference to FIG. 2, fins 132 in accordance with the present disclosure are shown. Fins 132 are included within each of the flow passages 110 and fins 134 extend from the flow passages 110. The fins 132, 134 form a solid matrix to provide thermal and structural connection. Fins 132 provide increased heat transfer in a direction from the inlet 120 to the outlet 122. Straight fins 132 a are positioned proximate the inlet 120 where creep and transient thermal stresses are greatest. The straight fins 132 a transition to shaped fins 132 b at the outlet 122 where enhanced thermal performance is desired. Positioning straight fins 132 a at the hottest regions reduces peak temperatures and associated creep, and peak temperature gradients and associated thermal stresses, which in turn will provide a longer life span for the heat exchange device. The shaped fins 132 b allow for increased extended secondary heat transfer surface area or increased heat transfer coefficient, which is more desirable at the outlet 122. With the variation in fins 132 a, 132 b, the device allows for peak metal temperatures and thermal transient stresses that are limited such that the device meets specified life requirements for a specified set of operating conditions or duty cycle. Fins 132 can be within each flow passage 110 and/or adjacent each flow passage 110. This allows the metal temperature in any given region of the device to be affected by the heat transfer characteristics of the heat transfer elements on both the hot and cold fins. While varying heat transfer characteristics on just the inlet side alone can solve the temperature and stress problems, varying heat transfer characteristics on both inlet and outlet sides or even just the outlet side is also suitable. The optimal configuration will depend on the specific design. For example, cost or manufacturing constraints could result in various design configurations.

In certain embodiments, a first predetermined number of straight fins 132 a can be positioned proximate the inlet 120. An intermediate section of the flow passage 110 between the inlet 120 and outlet 122 can include a second predetermined number of straight fins 132 a and a third predetermined number of shaped fins 132 b, where the second predetermined number of straight fins 132 a is greater than the first predetermined number 132 a. Proximate the outlet 122 a fourth predetermined number of shaped fins 132 b can be included that is less than the third predetermined number of shaped fins 132 b. Those skilled in the art will recognize that the variation of fins as shown and described in FIG. 2 can extend to various embodiments of heat exchanger devices without departing from the scope of the present disclosure.

With reference to FIG. 3, one embodiment of a heat exchange device 100 is shown. The device includes a first section 102 and a second section 104. The first and second sections 102, 104 are two identical heat exchange plate core sections each made up of flow passages 110 configured for heat exchange between heat exchange fluid within the flow passages 110 and fluid external of the fluid passages 110. Each of the flow passages 110 includes an inlet 120 and an outlet 122 (as shown in FIG. 2) with a bend or loop 130 at the outer edges of the device 100 to return the fluid to a center manifold 106. The bulk of the heat transfer occurs within the flow passages 110 of the first and second sections 102, 104.

The center manifold 106 separates the first and second sections 102, 104 and is configured to allow high pressure fluid to enter the manifold 106 at one end 112, pass into the flow passages 110 on either side of the manifold 106, and return to the manifold 106 to exit the manifold 106 at the opposite end 114. More specifically, the center manifold 106 includes a first plenum 112 a at one end and a second plenum 114 a on an opposing end. Fluid flows into the first plenum 112 a of the center manifold 106, passes through a respective fluid inlet 120 of a flow passage 110, follows a bend/loop 130 of the flow passage 106, enters the center manifold 106 again through the fluid outlet 122 and then exits the center manifold 106 through the second plenum 114 a. The design for the first and second sections 102, 104 and the center manifold 106 facilitates installation of the proposed heat exchange device 100 in place of an existing tube-shell unit.

The methods and systems of the present disclosure, as described above and shown in the drawings, provide for a heat exchange device with superior properties including heat transfer enhancements. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure. 

What is claimed is:
 1. A heat exchange device, comprising: a plurality of flow passages, each flow passage having an inlet and an outlet configured for hot fluid flow in a direction from the inlet to the outlet; and secondary heat transfer elements within and adjacent each flow passage having heat transfer characteristics varying in the direction of the hot fluid flow such that peak metal temperatures, associated creep, and transient thermal stresses are limited to values producing acceptable life of the device.
 2. The heat exchange device of claim 1, wherein the heat transfer elements are positioned proximate the inlet and the outlet and gradually transition from straight heat transfer elements at the inlet to shaped heat transfer elements proximate the outlet.
 3. The heat exchange device of claim 1, wherein proximate the inlet of each flow passage includes a first predetermined number of straight heat transfer elements.
 4. The heat exchange device of claim 3, wherein an intermediate section between the inlet and outlet of the flow passage includes a second predetermined number of straight heat transfer elements and a third predetermined number of shaped heat transfer elements, wherein the second predetermined number is greater than the first predetermined number.
 5. The heat exchange device of claim 4, wherein proximate the outlet of the flow passage includes a fourth predetermined number of shaped heat transfer elements greater than the third predetermined number of shaped heat transfer elements.
 6. The heat exchange device of claim 1, wherein the shaped fins include wavy fins.
 7. The heat exchange device of claim 1, wherein the shaped fins allow for increased extended secondary heat transfer surface area.
 8. The heat exchange device of claim 1, further comprising: a first section and a second section, each of the first and second sections including the flow passages, wherein each flow passage includes heat transfer elements positioned therein to provide increased heat transfer in a direction from the inlet to the outlet.
 9. The heat exchange device of claim 8, wherein the first and second sections includes plate sections in a stacked arrangement with each of the flow passages having a bend at an outer edge of the heat exchange device configured to return high pressure fluid to a center manifold.
 10. The heat exchange device of claim 9, wherein the center manifold includes a first plenum at one side configured to allow fluid to enter the center manifold and a second plenum on the opposing side configured to allow fluid to exit the center manifold.
 11. The heat exchange device of claim 10, wherein fluid flows through the first plenum into an inlet of a respective flow passage within the first and second sections, enters the center manifold through an outlet of the respective flow passage, and exits the center manifold through the second plenum.
 12. A heat exchange device, comprising: a first section and a second section, each of the first and second sections including flow passages configured to cool fluid, each of the flow passages having an inlet and outlet wherein each flow passage includes heat transfer fins positioned proximate the inlet to the outlet, the fins transition from straight fins proximate the inlet to shaped fins proximate the outlet; and a center manifold disposed between the first and second sections, wherein hot fluid enters the manifold at a first plenum, passes through the first and second sections and exits the center manifold at a second plenum.
 13. The heat exchange device of claim 12, wherein the shaped fins include wavy fins.
 14. The heat exchange device of claim 12, wherein the shaped fins include herringbone fins.
 15. The heat exchange device of claim 12, wherein the shaped fins allow for increased extended secondary heat transfer surface area. 